Re: Pole pig questions

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Bunnykiller by way of Terry Fritz <teslalist-at-qwest-dot-net>" <bunikllr-at-bellsouth-dot-net>

Tesla list wrote:

>Original poster: "by way of Terry Fritz <teslalist-at-qwest-dot-net>" 
><beans45601-at-themail-dot-com>
>
>If a pole pig is rated for 14.4kv 5kva, what does this mean? I know the kv 
>means kilo volt, but what does the kva mean? Is this like amps? Also, how 
>would you go about using a variac to limit the amount of power that goes 
>in. Also, how do you go about using an arc welder as a current limiter? 
>What are the pros and cons of using heater elements or lots and lots of 
>wire as a current limiter? Do the power companies sell pole pigs? How 
>would you go about getting one from a power company?
>Thanks
>Adam
>__________________________________________________________________
>
>
Hi Adam...

you are right about the kv part...

as far as KVA ...that means kilovoltsamps   kinda like watts in a dc 
system...   you use the kva part to figure out the amperage of the 
transformers rating to a rough degree....     to find the amperage of a 
14.4KV piggie at 5KVA  you divide the kva by the volts   example
5000/14,400    = .347 amps ( this is the secondaries output current)
a familiar sound would be like the NST    15kv -at- 60ma    the 14.4KV 5KVA 
unit would be like saying      14.4kv -at- 347mA

now that you know what the secondary output is in amps    you can now 
figure out the needed input amps at the supply voltage to the pig...
since most 14.4kv pigs use 240-280 volts in ...    you can find the input 
amps in two common manners

either  divide the 5KVA by the input voltage or ( a bit more mathematically 
inclined version)  divide the 14.4KV by the input voltage and then multiply 
by the output amps of the piggie

examples...

5000/240 = 20.82 input amps
14.4kv/240 = 60      60 X .347= 20.82

using a variac to control the input current to a piggie isnt quite all that 
simple  if you use a variac as  a current controller you have to be careful 
not to turn th variac to the stop points.. ( full on... this will fry the 
variac) ...   best to use an inductor ...   but to control a piggies 
voltage with a variac is easy...  just use the variac as normal  just be 
sure to use a variac rated for 25A   ( a 1256D is a good one to use) if you 
have a couple of smaller variacs ( rated for 15A each) you can paralell 
them for current sharing.

welders can be used as a current limiter  BUT you have to find one that can 
handle the current in the primary side of the welder for extended periods 
of time...  most cheap small welders have something called a duty 
cycle...   this is an on/off time  most welders have a duty cycle of 20% at 
full amp setting ..   20% on 80% off during a "normal" welding time cycle 2 
minutes on , 8 minutes off...

the welder is used in a manner that one of the input lines voltage is in 
series with the piggie and the secondary side of the welder is normally 
shorted.   example    the hot lead from the wall ( black) goes into the 
welder the other hot lead from the wall ( considering most welders are 
240VAC) goes directly to one of the inputs of the piggie...
backtracking a bit ...  the hot line on the welder that would normally go 
to the other hot lead on the wall is redirected to the piggies other 
input... thus completeing the circuit.

By changing the amp setting on the welder, the current is limited to the 
piggie in a rough manner...

as far as using heater cores ( resistive) or long wires etc ( still 
resistive) you develope emmense amounts of heat in the "element" ... yes it 
does divert current from the piggie to the "resistive element" But it also 
reduces the voltage to the piggie.... thus reducing voltage to the primary 
and this leads to wimpy streamers...   this is the con part....    the pro 
part is that inductors have a tendency to produce something called bucking 
( or surging , oscillations)  and the "resistive" elements doesnt 
...   altho I use stricktly inductive ( to a degree... the amount of wire 
on the inductor is somewhat resistive) I havent had any problems with 
bucking...

Some companies sell them as refurbished, exxpensive ....    check out 
ebay    check the Tesla list ...   it wont be cheap  ( well the piggie 
might be cheap but shipping will be pricey)


Scot D